The present invention relates to a self turn-off type semiconductor switch in which pulsing means is connected in series between the collector and emitter of a transistor TR and the series combination of the pulsing means and the transistor is connected in parallel between the main current electrodes of a thyristor CR, thereby moderating the characteristic condition of the transistor TR; and the collector of the transistor is connected in common potential to the reverse gate side main current electrode of the thyristor thereby easily using controlling means in common and easily using one case for packing the semiconductors and easily applying high voltage in large current.
It has been difficult to obtain a high voltage large current device from a transistor switch because it is difficult to attain the feeding of the base current, and the control for a large current device. A thyristor should have a complicated forced commutating means.
It has been difficult to obtain a large power device from a gate turn-off thyristor because the turn-off switch power is locally applied. Accordingly, it has a smaller capacity than that of the transistor.
Referring to FIG. 1, the conventional transistor switch will be illustrated.
In the conventional transistor switch, a gate turn-off type thyristor GTO is connected between the collector and base of the transistor TR. The transistor TR is turned on and off depending upon the gate turn-off type thyristor GTO. That is, the current amplification of the output of the thyristor GTO is controlled by the transistor TR.
Accordingly, the maximum power is dependent upon the transistor TR and the maximum power cannot be increased compared with that of the transistor. On the contrary, the controllable base current is limited by the thyristor GTO and accordingly, the power level is lower than that of the transistor switch having the other base controlling means.
It is necessary to increase the current amplification KFE of the transistor for decreasing the turn-off current of the thyristor GTO. Accordingly, the breakdown voltage is decreased or the current density per unit area of the semiconductor wafer is decreased.
In the conventional semiconductor switch of FIG. 1, the sum of the base voltage drop VBE of the transistor TR and the voltage drop VBE of the transistor TR and the voltage drop VAK of the gate turn-off thyristor GTO is the collector voltage VCE of the transistor. Accordingly, the voltage drop is high and the loss is large.
Moreover, the turn-off of the transistor TR immediately proceeds at the time of the turn-off of the thyristor GTO. Accordingly, the turn-off of the thyristor by the gate is not substantially improved for the thyristor, and it is dependent upon only the current amplification of the transistor.